Advanced Higher Chemistry 2009

it allows you to differntiate between two isomers in a racemic mixture

Reply 181

Meteorshower

Ok, the pH is 3.8 when half of the acid has been neutralized, so yeah you just do 10^-3.8 and you get the Ka.

But how can you tell when half of the acid has reacted?....

Reply 182

Dan11

it allows you to differntiate between two isomers in a racemic mixture

What's a racemic mixture? And what specifically is is it that differentiates the isomers?

Dan11

But how can you tell when half of the acid has reacted?....

the graph levels of when 18cm^3 of sodium hydroxide has been added, so halfway will be when 9 has.

Reply 183

OP

Meteorshower

No worries!

Can anyone explain to me what we need to know about plane polarised light and effects it has when passed through solutions :s-smilie:

Not sure about when it's passed through solutions but optical isomers spin the light in opposite directions. Never seen a question about solutions, didn't think we needed to know about that.

Reply 184

teabreak

Not sure about when it's passed through solutions but optical isomers spin the light in opposite directions. Never seen a question about solutions, didn't think we needed to know about that.

It's in a 2002 paper (managed to acquire some more past papers fortunately) so maybe the course has changed since. Can never be too careful though :p:

Reply 185

OP

Meteorshower

It's in a 2002 paper (managed to acquire some more past papers fortunately) so maybe the course has changed since. Can never be too careful though :p:

Can you post the question please?

Reply 186

if polarised light is passed through a solution, the chiral molecules turn the light in equal directions. eg. one in +50cm, the other in -50cm. If it is a racemic mixture the effect will be zero, as a racemic mixture contains equal amounts (50%) of each enantiomer

Reply 187

teabreak

Can you post the question please?

Q11 part c

Plane polarised light is not rotated when passed through an aqueous solution of X, suggest a reason for this.

Where X is propanoic acid with a hydroxyl group on the second carbon.

Reply 188

whats the answer.

im guessing cuz its a racemic mixture....

Yeah

yay!

would it be posible for u to post the answrers to the MC up please. (2002)

just like ACDCDDDDCED etc would be fine.

Thanks

Reply 192

OP

I know this is pretty simple but:

In the equation deltaG = -nFE, how do you work out the value of n?
I know it's to do with the number of electrons on some equation?

Reply 193

teabreak

I know this is pretty simple but:

In the equation deltaG = -nFE, how do you work out the value of n?
I know it's to do with the number of electrons on some equation?

Number of electrons on the reduction and oxidation ion electron half equations. Choose the larger number.

Dan11

would it be posible for u to post the answrers to the MC up please. (2002)

just like ACDCDDDDCED etc would be fine.

Thanks

CBBCCADABADDCBDDABDADACCBCBACC

31 a - CD
b - E
c - F

32 a - E
b - C
c - DF

33 AC

Reply 194

OP

Meteorshower

Number of electrons on the reduction and oxidation ion electron half equations. Choose the larger number.

Haha so easy :p:

Reply 195

teabreak

Haha so easy :p:

A lot of Ah chem is surprisingly easy - if you know what to do (if being the operative word :p:

)

Reply 196

OP

Meteorshower

A lot of Ah chem is surprisingly easy - if you know what to do (if being the operative word :p:

)

Yeah I know what you mean. A lot of the stuff is just beginning to click which is good. I just need to learn a few mechanisms and reagents. I still don't have a clue what to put if they ask me for a reagent!

Reply 197